/**
 * Copyright (C) 2011 Google Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.inject.internal;

import com.google.common.cache.CacheBuilder;
import com.google.common.cache.CacheLoader;
import com.google.common.cache.LoadingCache;
import com.google.common.collect.ImmutableList;
import com.google.common.collect.ImmutableSet;
import com.google.common.collect.Lists;
import com.google.inject.Binding;
import com.google.inject.Injector;
import com.google.inject.Key;
import com.google.inject.Stage;
import com.google.inject.spi.ProvisionListener;
import com.google.inject.spi.ProvisionListenerBinding;

import java.util.List;
import java.util.Set;
import java.util.logging.Logger;

/**
 * {@link ProvisionListenerStackCallback} for each key.
 *
 * @author sameb@google.com (Sam Berlin)
 */
final class ProvisionListenerCallbackStore {

    // TODO(sameb): Consider exposing this in the API somehow?  Maybe?
    // Lots of code often want to skip over the internal stuffs.
    private static final Set<Key<?>> INTERNAL_BINDINGS = ImmutableSet.of(Key.get(Injector.class), Key.get(Stage.class), Key.get(Logger.class));

    private final ImmutableList<ProvisionListenerBinding> listenerBindings;

    private final LoadingCache<KeyBinding, ProvisionListenerStackCallback<?>> cache = CacheBuilder.newBuilder().build(new CacheLoader<KeyBinding, ProvisionListenerStackCallback<?>>() {
        public ProvisionListenerStackCallback<?> load(KeyBinding key) {
            return create(key.binding);
        }
    });

    ProvisionListenerCallbackStore(List<ProvisionListenerBinding> listenerBindings) {
        this.listenerBindings = ImmutableList.copyOf(listenerBindings);
    }

    /** Returns a new {@link ProvisionListenerStackCallback} for the key.
     */
    @SuppressWarnings("unchecked") // the ProvisionListenerStackCallback type always agrees with the passed type
    public <T> ProvisionListenerStackCallback<T> get(Binding<T> binding) {
        // Never notify any listeners for internal bindings.
        if (!INTERNAL_BINDINGS.contains(binding.getKey())) {
            return (ProvisionListenerStackCallback<T>) cache.getUnchecked(new KeyBinding(binding.getKey(), binding));
        }
        return ProvisionListenerStackCallback.emptyListener();
    }

    /**
     * Purges a key from the cache. Use this only if the type is not actually valid for
     * binding and needs to be purged. (See issue 319 and
     * ImplicitBindingTest#testCircularJitBindingsLeaveNoResidue and
     * #testInstancesRequestingProvidersForThemselvesWithChildInjectors for examples of when this is
     * necessary.)
     * 
     * Returns true if the type was stored in the cache, false otherwise.
     */
    boolean remove(Binding<?> type) {
        return cache.asMap().remove(type) != null;
    }

    /**
     * Creates a new {@link ProvisionListenerStackCallback} with the correct listeners
     * for the key.
     */
    private <T> ProvisionListenerStackCallback<T> create(Binding<T> binding) {
        List<ProvisionListener> listeners = null;
        for (ProvisionListenerBinding provisionBinding : listenerBindings) {
            if (provisionBinding.getBindingMatcher().matches(binding)) {
                if (listeners == null) {
                    listeners = Lists.newArrayList();
                }
                listeners.addAll(provisionBinding.getListeners());
            }
        }
        if (listeners == null || listeners.isEmpty()) {
            // Optimization: don't bother constructing the callback if there are
            // no listeners.
            return ProvisionListenerStackCallback.emptyListener();
        }
        return new ProvisionListenerStackCallback<T>(binding, listeners);
    }

    /** A struct that holds key & binding but uses just key for equality/hashcode. */
    private static class KeyBinding {
        final Key<?> key;
        final Binding<?> binding;

        KeyBinding(Key<?> key, Binding<?> binding) {
            this.key = key;
            this.binding = binding;
        }

        @Override
        public boolean equals(Object obj) {
            return obj instanceof KeyBinding && key.equals(((KeyBinding) obj).key);
        }

        @Override
        public int hashCode() {
            return key.hashCode();
        }
    }
}
